Why do I get the message "This disk cannot be used to start your computer" w/ upgrade to Mountain Lion from 10.6.8

Question

I have a MacBok pro later than 2007.  running 10.6.8 .  Downloaded Mountain Lion from app store.  When  I get to the install page I get the message "This disk cannot be used to start your computer."  What is the problem and what can be done?
Thanks,

Answer 1

I appreciate the prompt reply.  I saw that on the support community and it isn't giving me a solution.  
The disk where the volume I need to upgrade is 250.06 GB Hitachi, the partition window (current) does not have a blue marker for the used data space, so there is no way to resize it.
If it's helpful, System profiler reads:
NVidia MCP89 AHCI:
  Vendor:          NVidia
  Product:          MCP89 AHCI
  Link Speed:          3 Gigabit
  Negotiated Link Speed:          1.5 Gigabit
  Description:          AHCI Version 1.30 Supported
Hitachi HTS545025B9SA02:
  Capacity:          250.06 GB (250,059,350,016 bytes)
  Model:          Hitachi HTS545025B9SA02                
  Revision:          PB2AC60W
  Serial Number:          100814PBL200CSJA72PN
  Native Command Queuing:          Yes
  Queue Depth:          32
  Removable Media:          No
  Detachable Drive:          No
  BSD Name:          disk0
  Rotational Rate:          5400
  Medium Type:          Rotational
  Partition Map Type:          GPT (GUID Partition Table)
  S.M.A.R.T. status:          Verified
  Volumes:
  Capacity:          209.7 MB (209,715,200 bytes)
  Writable:          Yes
  BSD Name:          disk0s1
  Capacity:          249.72 GB (249,715,376,128 bytes)
  Writable:          Yes
  BSD Name:          disk0s2
Macintosh HD:
  Capacity:          249.71 GB (249,714,352,128 bytes)
  Available:          100.41 GB (100,405,456,896 bytes)
  Writable:          Yes
  File System:          Journaled HFS+
  BSD Name:          disk0s2s1
  Mount Point:          /
Boot OSX:
  Capacity:          134.2 MB (134,217,728 bytes)
  Writable:          Yes
  BSD Name:          disk0s3